We have been fortunate in our almost 20 years of cruising. Once it rained in St Thomas for a few minutes, then stopped which is normal in the tropics. But, in Grand Cayman it stormed all day,and badly. We were going to gett off, but as we made our way to the gangplank, we saw people looking like drowned rats, and had 2nd thoughts
Go to the dollar store and buy the plastic ponchos,and a small travel umbrella, and if you don't get the downpour that we did, get off, and enjoy.
It would be unusual for a ship not to dock, due to this type of scenario.
Have a great cruise!